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Role in Future Electric System Planning

News Release: NREL Research Determines Integration of Plug-in Electric Vehicles Should
Play a Big Role in Future Electric System Planning

Jan. 22, 2018

An influx of plug-in electric vehicles (PEVs) charging without coordination could
prove challenging to the nation’s electric grid, according to research conducted by
the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL).

“Realizing the full benefits of vehicle electrification will necessitate a systems-level
approach that treats vehicles, buildings, and the grid as an integrated network,”
said Johney Green Jr., NREL’s associate lab director for Mechanical and Thermal Engineering
Sciences.

NREL engineer Matteo Muratori, author of the new Nature Energy paper "Impact of Uncoordinated
Plug-in Electric Vehicle Charging on Residential Power Demand," said his research
points to key areas where additional investigation is warranted. (Photo by Dennis Schroeder/NREL)

“Previous research into the amount of energy required by homes hasn’t taken into account
plug-in electric vehicles,” said Muratori, who holds a Ph.D. in mechanical engineering.
“Given that more people are choosing to drive these types of vehicles and charging
them at home, this additional demand should not be overlooked.”

The simulation concluded that a PEV market share of up to 3 percent, which translates
to about 7.5 million vehicles, does not significantly impact the aggregate residential
power demand. More than 600,000 plug-in electric vehicles were already on the road
at the end of 2016, a figure that includes about 150,000 sold during the year.

Muratori also looked at the impact PEV charging might have on a residential distribution
transformer. In this case, a problem arises when motorists gathered in a geographic
area began buying these vehicles and plugging them in to recharge upon returning home—a
practice known as uncoordinated charging. Even without large numbers of PEVs on the
road, this clustering effect “will significantly increase the peak demand seen by
distribution transformers and might require upgrades to the electricity distribution
infrastructure,” according to Muratori’s paper.

The research also looked at whether the household used the less-powerful Level 1 charging
option or the more-powerful—and therefore faster—Level 2 charging option. Muratori
found that as more PEVs are added to a neighborhood, and a higher charging power is
adopted, “the distribution infrastructure might no longer reliably support the local
electricity demand.” He also noted the higher demand could shorten the expected life
of a transformer.

The electric load profiles used in this paper, including household demand and PEV
charging with a 10-minute resolution, are available for download here.

Earlier studies on how PEVs might affect the grid assumed utilities would have some
control over when charging occurs, referred to as coordinated charging, which will
greatly facilitate PEV integration. Muratori noted that might be true in the future,
but not necessarily. His research didn’t focus on using PEVs to return a battery charge
to the grid to increase the reliability of the electric system. Future research, Muratori
said, should focus on understanding consumer behavior to determine charging requirements,
and the choice between using Level 1 and Level 2 residential charging equipment.

“Matteo’s work raises important issues for a world with increasing electrification
of the vehicle fleet, and leaves us with clear avenues for additional research,” said
John Farrell, NREL’s laboratory program manager for vehicle technologies. “We need
to continue looking at the synergies between electric vehicles and buildings, especially
to make sure the grid remains safe and resilient.”

NREL is the U.S. Department of Energy's primary national laboratory for renewable
energy and energy efficiency research and development. NREL is operated for the Energy
Department by The Alliance for Sustainable Energy, LLC.